I've worked on similar stuff in the past at Google and you couldn't be more wrong. For example, if your CPU screwed up an AES calculation involved in wrapping an encryption key, you might end up with fairly large amounts of data that can't be decrypted anymore. Sometimes the failures are symmetric enough that the same machine might be able to decrypt the data it corrupted, which means a single machine might not be able to easily detect such problems.

We used to run extensive crypto self testing as part of the initialization of our KMS service for that reason.