Tidal Boon says: "If Dahan are pushed to your ocean, you may move them to any Coastal land instead of Drowning them."

The phrasing of the card is very important. "Your ocean" means this effect only applies if Ocean's Hungry Grasp has Presence in that ocean itself. If Ocean's Hungry Grasp does not have Presence in the ocean itself, then the Dahan are Drowned.