Albert Barnes Commentary 2 Kings 10:11

"So Jehu smote all that remained of the house of Ahab in Jezreel, and all his great men, and his familiar friends, and his priests, until he left him none remaining." — 2 Kings 10:11 (ASV)

So Jehu slew - This should be translated, “And Jehu slew.” The reference is to new executions (compare 2 Kings 10:17). He proceeded on his bloody course, not merely destroying the rest of Ahab’s relatives, but also putting to death all of Ahab’s most powerful partisans.

His priests - This does not refer to the priests of Baal in general, whose persecution came later (2 Kings 10:19), but only to those who were attached to the court.