Maybe when you place it, you could set the server ip and then only the player that placed it would be able to use it, anyone else would need permission.
Very interesting, I like the direction this is going. Sort of like an MMO, I like it. What would be really cool in this system would be to eventually have a portal, say some block you could place inside your property that could teleport your party or just you back to your own personal server/world. An example: "hey come check out my world, I have a cool blueprint you can clone."