I do two things that might not be mentioned otherwise:
1. I have an end of workday regular, scheduled transition activity that occupies my mind - something stupid and simple (online multiplayer video game with tournaments that start at 5 and 7pm locally each day). I try to get work wrapped up enough to break away at 5pm and start a tournament most days. If it's a particularly busy day, I try for the 7pm. It occupies my mind for 30 mins or so, and in combination I play YouTube videos in the background. It's long enough to break the chains from the day's activities and set me up for a good night most days.
2. Learn to use the sleep functionality on your computer. At the end of the day, I deliberately toggle it on and it feels like a tangible "end" to the day.
Not always successful, but works enough of the time. And most importantly... Know that your company DOES.NOT.GIVE.A.SHIT.ABOUT.YOU. and let that drive your courage to push that sleep button at the end of each day.