Both grs#1 and grs#2 are almost certainly from the same original lemma, the etymon of various nouns for "crushed grain." Here the metaphoric meaning of "to go through something in a very finely detailed manner" has prevailed. In grs#2 the literal meaning "to crush" has been generalized (in the D stem) as "to destroy" and then an intransitive formed by back-formation as the G in Syriac.