Too late & too tired to write this up now, but I'll do it up after I get home from work, in about 10 hours.
BTW: Do you want the results shown to all in channel, just to you in channel, via a custom window, a dialog box or some combination there of.
Additionally, how are you defining the difference between local and global. If global is a match across all networks that you're on, note that it's possible for two different people to be using the same nick on two different networks, so your Global common channels won't technically be 100% correct.
On the other hand, if you mean local, as in on the same server that you're connected to, and global meaning all of the interlinked servers creating the network, this will be more difficult, and I believe, will require you to have IRCops level status on the network (referencing UnRealIRCd)
You can echo it to a custom window. As far as different people using the same nick on different networks, that's fine.
