allowDuplicateDomains is just a crutch for tests. Applications rarely start more than one cache manager in the same JVM, and when they (e.g. multiple applications in an application server) do it's always a good idea to give each cache manager a unique name.

Our test suite doesn't really need allowDuplicateDomains either: TestCacheManagerFactory adds a UUID to the domain name, unless the test has explicitly set a (presumably unique) domain name.