In a true multi-server domain (i.e. not just a collection of servers each with the proposed first-stage standalone server domain) a new node joining should get its configuration from a "central point"; whatever it has locally on disk when it first starts should be replaced. In Westford we discussed that any of the running servers in the domain whose profile has the required capability could act as that "central point", with an HASingleton-like mechanism used to determine which node is currently taking on that role.
The node joining the domain would need to know enough to contact the domain to get its config; such info would presumably be provided via the command line (or perhaps a simple properties file). I envision that working somewhat like HA-JNDI does now; the client is (optionally) provided a set of well-known URLs to contact, (optionally) falling back to multicast discovery.