make clean (really!)

Hello, i try to build the newest snapshot while still having an old one on the disk. Unfortunately, 'make setup' crashes when looking for Cross Tools. Anyway, i don't think it has something to do with the new snapshot, but some hidden setup files storing my old config. Because, when i rename my old snapshot and then try to rebuild it, it crashes as well. So, how do i make the setup really clean? 'make clean' seems not enough, since it still knows some old configs. Where are those hidden files, and how to remove them? Thanks.