[steveklabnik]

The intention with Russian doll caching is that the cache uses LRU, so you don't need to worry about clearing the cache. No poison pill needed. Memcache operates this way.

Given that there's an 'lru' folder with a package that says 'implements a LRU cache' as the first comment, I assume this works that way as well.

[grey-area]

Yes in a perfect world you never need to clear everything, but sometimes it's useful for testing or to allow end users to clear the cache in case of caching bugs.