You can change and assign the mastership of users and user groups
in your MultiSite environment as users and groups are created
or changed.
Mastership issues when creating users and groups
Although administrators can create users and groups at any site
so that they are mastered at the local site where they are created, new users
and groups are only propagated from the schema repository to a user database
at the working master site, and they are propagated only if they are mastered
at the working master site. Users and groups should only be created at the
working master site to avoid propagation problems.