Q. The other day I was asked about why (in a single forest, multiple domain environment with separate SMS hierarchies in each domain) does a SMS client get assigned to an SMS site in the wrong domain.
A. If you have multiple domains in your forest, and multiple independent SMS hierarchies, although the schema is extended for your entire forest, each domain maintains its own System Management container in Active Directory in its own domain partition. A domain controller does not replicate its System Management container to other domains in the forest. However, the Systems Management information from each domain is published to the global catalog for the forest, When SMS clients use automatic site assignment, the global catalog returns information for all sites in the forest, regardless of the domains in the hierarchy affiliation. This means that if two sites, installed in separate domains in the forest, have overlapping site boundaries, the client could potentially be assigned to the wrong site. This is one reason that an overlapping site boundary is not recommended.