37.6.1.2. Can caches snoop data from other caches?
Either they can snoop only control, or both control and data can be snooped.
The answer to this determines if some of the following design decisions make sense.
This is the central point in question at: https://electronics.stackexchange.com/questions/484830/why-is-a-flush-needed-in-the-msi-cache-coherency-protocol-when-moving-from-modif
If data snoops are not possible, then data must always to to DRAM first.