Mapping cache for particular DB is stored on a server (SS/SC) as long as mappings are not modified for that database (or server restarted). But there are some more cases when it should be invalidated. I plan to add the following:

• database is created (it may be overwrite operation or old database file removed using OS tools);
• database shutdown status changes (when database is shutdown file might be replaced by another with same name);
• nbackup restore is complete;

I can not detect a case when file is replaced by OS tools w/o prior DB or server shutdown because it requires opening file on each cache access which is avoided by normal check operation. Want to mentions that such trick was never recommended to do i.e. no new restrictions added here.