The first architecture to consider is that of the Global Enterprise Service Bus. In this pattern, requests for service access are first processed by the local ESB. If not resolved , the request is then forwarded to the Global ESB, which in turn routes the request to the ESB instance able to handle the request.
This pattern offers a consistent routing approach in which each ESB's content based routing rules simply route to the global bus if a request cannot be resolved. It does however have some major drawbacks: it is a central point of failure and traffic on the Global bus could act as a choke point for the entire SOA.