I was running aptitude and previewing packages marked to be updated when the power went out for a second. Now almost all of my installed packages are marked as obsolete and the updates I was about to install aren't found anymore. Updating the package list doesn't have any effect.
I assume I need to delete some file in the apt cache so that the package lists are downloaded anew. Is this assumption right? If yes, which file would I need to get rid of? If no, what do I need to do instead to repair my dpkg/apt?