The 1108 had simplistic memory protection and didn't have cache so there was no concerns around cache coherency. The 1100/80 which came 15 years later finally i

The 1108 had simplistic memory protection and didn't have cache so there was no concerns around cache coherency. The 1100/80 which came 15 years later finally introduced a cache that was really just a buffer and, to my knowledge, had no coherency scheme largely because of the way the architecture of those systems worked. The Alpha team was working on a much more sophisticated system and had to solve a much coherency problem. Weaker models allow greater throughput and save transistors (and reduce power/heat) at the expense of more carefully written software and operating systems.