What is the proper syntax to tag (@ mention) a user on a different instance?

Vampire [any]@hexbear.net to Asklemmy@lemmy.ml – 23 points –

e.g. [@Dirt_Owl@hexbear.net](https://hexbear.net/u/Dirt_Owl) would mention a hexbear user on hexbear

But if I'm posting on Instance A, tagging a user with an account on Instance B, do I change the first part of the link only? Or both? What is the correct syntax please and thank you.

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