Yes. You can delete keys. But you need to know the name of the key. You could not use some kind of tagging ("these keys are related to component A" and later "invalidate all entries related to component A")

Using memcaches expiration is what the article does. But I was referring to the requirement of real-time data. If the source data changes, you might want to see the new data and not have to wait for the caches data to expire.

people normally kick off a background job to update the cache and not wait for it to expire. It still isn't instantly consistent, but it's usually close.