tom hardware seems to have the best epyc hotchips coverage i have seen so far:
http://www.tomshardware.com/news/amd-threadripper-epyc-mcm-cost,35306.html
Not alot new, but there are quite a few slides on the Memory/cache/Io systems.
There's a slide that offers a bit more information on Zen's MDOESFI coherence protocol.
Above what was present in MOESI, the D state is defined as Dirty and listed as some kind of migratory sharing optimization.
It may be that F is Forwarding, like in MESIF, but it's not clear if that is the case.
That's taking AMD's protocol into a notably higher number of states than for its older architectures and Intel's, although short of the double digits of IBM's.
The slide doesn't quite get into what it takes for a line to go into the D or F state.
One possible interpretation is that AMD's protocol is trying to optimize the clean and dirty sharing paths. Under its MOESI protocol, there was some later wrinkles to the shared state, such as there being a little-discussed optimization for sharing where the requester got a shared line in the Owned state, and a potential state that was either in the caches or an intermediate directory/cache state that tried to optimize for sharing dirty lines that were to be modified shortly after (lock variables, etc).
Perhaps this has taken those optimizations and made them more formal. Another possibility, if AMD's choice is more like IBM's philosophy, there is information baked into these states about locality or probability of sharing.
http://techreport.com/news/32459/amd-ships-revised-ryzen-cpus-with-a-compile-bug-fix
Fixed hardware version for that previously discovered bug apparently.
Presume its just that later stepping thats used in Threadripper/Epyc -> AMD must have seen the bug & started to fix before Ryzen went live?
Various reports indicate it doesn't need a new stepping, just a more recent production week like 25 or later.
That might mean there's some other way to make a small change on-die, or it's related to something besides the masks like new tests or changes in configuration or the packaging. Since this seems so inconsistent even among older chips, it might be discarding dies that were passing validation when they shouldn't. That may explain why the highly binned Threadripper is supposedly immune despite having B1 stepping just like Ryzen, although other elements like packaging and fuses may be different as well.