cache coherence problem

Difference between Write invalidate protocol & Write Update Protocol (Bus-Snooping )

https://www.geeksforgeeks.org/difference-between-write-invalidate-protocol-write-update-protocol-bus-snooping/

https://techexpertise.medium.com/cache-coherence-problem-and-approaches-a18cdd48ee0e

https://www.sciencedirect.com/topics/engineering/cache-coherence