Not super easily. It can be done by querying the postgresql dabase, but there is no built-in method to do it using the browser interface at the moment. When anyone from any instance does report them, you will see the report.

Someone please correct me if I am wrong. But, as far as I am aware, if you purge a user from your instance, that action is federated to every other instance - so if you respond quickly to these reports, other instance's admins will not need to deal with them themselves. It is only when you perform an action on a user from a different instance that the action is only local.