It appears that snooping is a common technique in "shared channel communications", for example, in computer networking, snooping is also used: https://en.wikipedia.org/wiki/IGMP_snooping

Directories make for "scalable" cache coherence because only the processors for whom a certain cache line state is relevant at a given point in time need to get that info from the directory. In snooping, all processors use one interconnect through which any cache coherence message travels, even if only one or two processors actually care about that broadcast message.