Resetting iTunes Library As If The First Time

This may seem pathetically obvious. How do I reset iTunes to look at a library of music as if it was new for the first time. I have been reconciling two different libraries on two systems and have created a unified library. But when itunes goes to that folder, it doesn't look for the next combined music, just the stuff it knew before. I'd like iTunes to take a new look at the whole folder and treat it all like it was a new install with a "first import" approach to get all the new tunes in the library. Make sense?