As a feature request, this might require some client-side processing. I have seen similar asks in other communities, though.
A interesting UX to test this, if it were possible, mkght could be something like:
[Post title]
[All Lemmy instances/communities to which a user has subscribed that this post exists.]
[Post content]
Etc.
While this may not be an easy implementation, it would interesting to test on Jerboa.
Ah! A Chilean vegan, I see.