In the past I switched my repository, had two for a while, then removed all traces of the old/unused one.
I've scanned just about every file (Sourcetree settings/app data/.git folder/git settings, windows credential manager etc) and cannot find any trace of the old repository, however sourcetree keeps asking for the password for it (via Windows credential manager, and then when I cancel by a sourcetree pop-up). It is rather annoying as these pop-ups just keep on coming.