Or various combinations of snooping and directories ("snoop filters", or directories that act as "bridges" between broadcast domains, etc.).
In current Xeon processors (and presumably AMD EPYC as well, thought I don't yet have first-hand experience with those), you have a couple of directories per CPU with snoop filtering, as with tens of cores broadcasting becomes a scalability bottleneck. In the BIOS you can change the mode how it operates, with slightly different names and semantics depending on the CPU generation.
No, it can be implemented with directory instead, e.g.
https://en.wikipedia.org/wiki/Directory-based_cache_coherenc...
Or various combinations of snooping and directories ("snoop filters", or directories that act as "bridges" between broadcast domains, etc.).
In current Xeon processors (and presumably AMD EPYC as well, thought I don't yet have first-hand experience with those), you have a couple of directories per CPU with snoop filtering, as with tens of cores broadcasting becomes a scalability bottleneck. In the BIOS you can change the mode how it operates, with slightly different names and semantics depending on the CPU generation.