It seems it's currently possible to do:
Resulting in a file published in the local environment referencing a foreign environments cluster+group.
There was no intention to support this and it causes problems and inter environment scans when files are referenced.
The only place I've seen it happen was in test code.
And the symptom was to cause processes that scanned files and hit files like this to try to contact the Dali which if down (or non-existent) would stall and eventually fail.