Green’s Dictionary of Slang

(US prison) to maintain prison discipline and rules.

1918		H. Simon ‘Prison Dict.’ in AS VIII:3 (1933) 30/1: POLICE. 1. To clean up. [Military.] 2. To beat up.
2000		Other Side of the Wall: Prisoner’s Dict. July 🌐 Policing: An officer who is doing his or her job. ‘That officer is policing hard.’.