To transfer ownership of all documents from one user to another:

1. Sign in to the Google Admin panel. 2. Click the Settings tab, and then click Drive and Docs in the left column. 3. Click the Tools tab and complete the Document ownership transfer section:

• In the From field, enter the user name of the current owner and select the user’s domain.
• In the To field, enter the user name of the new owner and select the user’s domain.
  
  

Tip: If the transfer involves a very large number of documents, you may want to notify the new owner and check that they have enough storage capacity to accommodate the transferred documents. (In the new owner's Google Drive on the web, click the Upload button to see the amount of storage used/available). 4. Click Transfer documents to save.

All of the transferred documents are automatically organized in a single new folder — titled with the previous owner’s email address — in the new owner’s Drive.

The administrator and the new and previous owners receive email about the transfer as soon as the process completes.

If there were any problems with the transfer (e.g. the new owner's quota is exceeded, which prevents the transfer of some documents), the email notification describes what happened. To fix the problem, you might purchase more storage for Google Drive for the new owner, transfer ownership of the documents to a different user, or redistribute ownership of documents one at a time to different users.

Does EXACTLY what you need. Just did it and it worked perfectly.

Source.

To transfer ownership of all documents from one user to another:

1. Sign in to the Google Admin panel. 2. Click the Settings tab, and then click Drive and Docs in the left column. 3. Click the Tools tab and complete the Document ownership transfer section:

• In the From field, enter the user name of the current owner and select the user’s domain.
• In the To field, enter the user name of the new owner and select the user’s domain.
  
  

Tip: If the transfer involves a very large number of documents, you may want to notify the new owner and check that they have enough storage capacity to accommodate the transferred documents. (In the new owner's Google Drive on the web, click the Upload button to see the amount of storage used/available). 4. Click Transfer documents to save.

All of the transferred documents are automatically organized in a single new folder — titled with the previous owner’s email address — in the new owner’s Drive.

The administrator and the new and previous owners receive email about the transfer as soon as the process completes.

If there were any problems with the transfer (e.g. the new owner's quota is exceeded, which prevents the transfer of some documents), the email notification describes what happened. To fix the problem, you might purchase more storage for Google Drive for the new owner, transfer ownership of the documents to a different user, or redistribute ownership of documents one at a time to different users.

Note, this only works if both users are in the same domain. You cannot transfer ownership between domains, which is what the original poster asked for.

Source.

http://support.google.com/a/bin/answer.py?hl=en&answer=1247799 - Does EXACTLY what you need. Just did it and it worked perfectly.

To transfer ownership of all documents from one user to another:

1. Sign in to the Google Admin panel. 2. Click the Settings tab, and then click Drive and Docs in the left column. 3. Click the Tools tab and complete the Document ownership transfer section:

• In the From field, enter the user name of the current owner and select the user’s domain.
• In the To field, enter the user name of the new owner and select the user’s domain.
  
  

Tip: If the transfer involves a very large number of documents, you may want to notify the new owner and check that they have enough storage capacity to accommodate the transferred documents. (In the new owner's Google Drive on the web, click the Upload button to see the amount of storage used/available). 4. Click Transfer documents to save.

All of the transferred documents are automatically organized in a single new folder — titled with the previous owner’s email address — in the new owner’s Drive.

The administrator and the new and previous owners receive email about the transfer as soon as the process completes.

If there were any problems with the transfer (e.g. the new owner's quota is exceeded, which prevents the transfer of some documents), the email notification describes what happened. To fix the problem, you might purchase more storage for Google Drive for the new owner, transfer ownership of the documents to a different user, or redistribute ownership of documents one at a time to different users.

Does EXACTLY what you need. Just did it and it worked perfectly.

Source.