Well, it's supposed to be getting the same data every time, even, potentially, on a flawed disc (in which case the data would be incorrect, but the same every time). So in order to detect it, he'd have to figure out a way to provide a disc that he knew would confuse the drive enough for it to read different data for the same sector at different times. And a disc that did that on one drive isn't necessarily going to do it on another.

So I'd say that it is definitely difficult to detect. Safest, once again, to have it clear the cache as needed, to assume there is one, even though it's slower.