It's called "Load, Dump, and Compare".
During the launch countdown, CVFS loads the onboard MMUs [Mass Memory Units], then their memory is dumped and the dump data compared to master tapes which are kept in a safe in the LPS room at KSC.
This is what we did in our program. We compared the data the satellite's computers to ground 'truth' images.
We took three dumps and compared the dumps to each other and then the ground info.
Memory can take radiation hits in space and change its contents.
But I bet the shuttle's computer are much more hardened than ours.