Different Boards, Sharing Common Forums, Possible?

[azn_romeo_4u]

For example,

All the websites are different domains, but when a user goes to the forum, it goes

Site1.com forum is on
------board1.mainsite.com
Site2.com forum is on
------board2.mainsite.com
Site3.com forum is on
------board3.mainsite.com
Site4.com forum is on
------board4.mainsite.com

All the boards are subdomains of the main site. But they share some common forums, but also have unique forums to that subdomain only.

T_T Hard for me to explain. For example, each of the boards, share like 10 common forums, where users across any of the domains can access. They all will share those 10 forums, but won't see the other forums that are made for their different sites.

Could this work with one ultra powerful server, and using load balancing? Is this is possible?

Besides the common forum, users online would be shared as well. Post count increases on those shared forums.