The address cache in Outlook. How do I empty it...?

Hi everyone!

I've come across the following problem: when I'm writing an email, and address it to 'Bill', Outlook puts a red line under it and wants to know which Bill. Nothing wrong with that, but...
some of the suggestions Outlook comes with are outdated and no longer present in my address book.
Who knows how I can get Outlook to empty/re-initialize the address cache it uses for this purpose?

Regards,
Evert