Handling assignment groups across multiple domains
When there are multiple domains under a parent domain, assignment groups may need to be shared across these child domains. For example, say there are four parallel domains: TOP/A, TOP/B, TOP/C, TOP/D. There might be a requirement to have a common assignment group to whom tickets from any of the four domains above can be assigned to.
Create a group on the TOP domain (which is the parent of A,B,C and D).
At this point if you have an assignment rule to assign to the newly created group, it should work.
If you want users across different sub-domains from the group to be able to assign tickets back to them:
All domain-separated instances
For more information, see the following product documentation topics: