It sorta depends on the relationship between federated servers. If your server acts as a data controller and the servers it federated with act as a data processor, then yes indeed your admin would have to contact all those servers to get that data removed.
But I don’t think that’s what the relationship really is. I think your server publishes that data effectively publicly. At that point other servers can take a copy if they want (ie each would be a controller). So you’d have to make a request to each server to get the data removed.
Think about it like this, if you allow some print publication to print your name for some reason, some other companies might keep a copy of that data. Eg an archival company, or perhaps something less nice like a sales leads company. The publication doesn’t have a responsibility to contact them all. Even if, say, they have some relationship, like federation, or for example archival company has a subscription to the newspaper.
So if you want that data deleting you’re going to have to contact every sever that has it.