Is Merged Mining implemented via the coin or the miner?

[CrimsonGT]

My understanding in the way that merged mining works is that the pool is configured to submit hashes against 2 block chains as opposed to just one. I have however noticed several CryptoNote coins forking to "add support" for it. Looking at various CryptoNote currencies, they seem to support MM with a select few other coins.

Is MM implemented at the coin level or would it be the miner simply checking the hashes in two places instead of one?