YB, Anyway, 3 Mb cache and 6.4 Gb/s seems to be a good basis for 4-way scalability, but the nothion that propriatery circuitry is in design to make it scaling further suggests that that's about it.
What's the big deal over "proprietary circuitry"? Intel's FSBs have always been limited to four processors per bus. To scale further would require multiple FSBs. Whether you use Intel's chipsets or "proprietary circuitry" to implement that is irrelevant.
Scalability has always been a function of many, many factors. Different architectures require different solutions for scalability. If you think Opteron's scalability comes for free, think again.
Tenchu