Cache consistency when using memcached and a rdbms like MySQL

Question

I have taken a database class this semester and we are studying about maintaining cache consistency between the RDBMS and a cache server such as memcached. The consistency issue

Answer 1

How about using a variable save in memcache as a lock signal?

every single memcache command is atomic

after you retrieved data from db, toggle lock on

after you put data to memcache, toggle lock off

before delete from db, check lock state