This is similar to a 'global' view, can be cached.
TBD:

• Push or pull model?
• Cache a view?

Possibly provide a hashmap of sites associated with lists of member addresses. On a SiteUp event, send a multicast message soliciting a response from every single member providing its address and possibly additional information. On reception of a response, the hashmap is updated.

On a SiteDown event, remove the site and all associated addresses from the hashmap.