I recently posted about changing stored credentials used by Visual Studio 2005 Team Explorer.
Removing the cache never really works in my opinion. The only two options I have found are:
This concurs with James Mannings entry here"We ended up shipping a tool called clearcreds.exe to help users that had checked this box wipe out the stored creds."
You can also looking additional information from MSDN for Visual Studio Team System concerningTroubleshooting Team Foundation Server Permissions and Security
While researching the problem I came across this cool add-in from Noah Coad. It helps you search Work Items!
Additionally Grant Holliday has created an Australian mailing list for TFS with a large subscription base.