There is a diagram of a process that reads the MySQL commit log and uses that to send Memcache delete commands. Not exactly groundbreaking.

But I would also guess that FB would have to explain lots of their middleware concepts in order to explain how data in the database maps to memcache keys defined in middleware.

Personally, I think the hard part is ensuring the entire company/system accesses data through the correct abstractions (eg. the newest data model code) and does not bypass the data model code (eg. by hitting the database directly).