ISM corruption

How does one go about and fix the ISM if it gets corrupted after a server crash? I've read my predecessor's notes and he's only written the easy way. He said it's not exactly the correct way. The steps involve renaming the index and mm folders and restarting ISM. Then he goes on to create the backup devices and runs a backup. On his notes, he said the previous backups become unusable but he also said that there are steps to make them usable. Sadly, he didn't write them down.