Many times this question comes to me in past and today I got a call from my friend working in previous organization for same thing. Same question is asked in MSDN forum also. So I decided to document this.

We can clear the recent items from the cache by Report Builder Options-> Clear All recent Items

But this will not remove the saved credentials for a particular report server or report server getting connected by default. This gets cached at below location for RB 3.0.

%userProfile%\AppData\Local\Microsoft\Report Builder\10.50.0.0

So, to remove cached data, we need to delete the file(s) from this folder. Please note that doing so, all the recent history and the custom settings (Grouping Pane, property Pane etc.) will be lost.