movement - RTS Game Protocol

I've been thinking about a multi player RTS game. The part that I can't seem to get around is keeping unit movement synced. If I move unit A to spot XY, I have to communicate that back to server that relays to the other client.

I'm curious what the communications would look like. Would you just communicate to the server that I'm moving unit A to XY from JZ? Maybe you need to communicate movement coord by coord instead? What's the most efficient methodology to communicate movement of units from one client to the other?

EDIT

This is a reposted question from stackoverflow. I found that this site was probably a better place for the question.

One of the better answers from that post:

I assume you're intending to use the Client-Server networking paradigm? In which case you cannot trust the clients to handle the actual positioning of units, you must delegate that task to the server. You then take the command list from each client per-tick, and compute the movement of each unit, once this has been completed, next tick you relay the position of each unit relevant to each client (either on a whole-map basis, or per-view basis), and start the process again.