I don't know how moderators communicate over cross site boundaries, but I'm sure that such migration action should be reviewed and confirmed by the target site moderators and go there in first place.
Actually, the standard recommendation to the moderators (from the CMs) is specifically to not ask a site mod before migrating:
You don't need permission to migrate questions, and definitely shouldn't be pinging moderators on another site every time you have something that needs migration.
While mods are an easy source of knowledge about a site, they're not the all-knowing, final deciders of site scope; the users are. As such, rejecting the migration can be done by any five users closing the question for any reason (duplicates will stay but be marked as duplicates). There's really no reason to get another moderator involved. Shog explains the process for migration here.
That said, like with any migration, the rule for moderators and regular users alike is "Don't migrate crap" and we generally hope that our fellow mods will at least look at the site guidance before migrating, particularly when trying to send something to a site they're unfamiliar with... but it's really not a big deal. But, if a question looks on topic and doesn't look like a horrible question, there's no real reason to wait on migrating it to get a response from a site mod on the target site.
Occasionally I've seen (and have done myself) that mods on a site will come and report in to the migrating moderator to let them know if a the question was a bad fit for the site, particularly when several questions were migrated that were bad fits... but clearing every migration before sending is unnecessary.
Just close and/or delete the question, or if you're not a mod/high rep user flag the post with the "other" option explaining the problem. That'll reject the migration.
If it keeps happening then the site mods can ping the other site's mods in TL to remind them to be careful when migrating that a) the question isn't just a bad question and b) it's actually on topic on the target site.
All mods should take the view that if there's any doubt about a migration then don't do it.