I have that icon. It doesn't close apps though, it only wipes my notifications.
While Googling I stumbled upon this though: http://android.stackexchange.com/qu...ckground-apps-at-once-in-android-5-0-lollipop
The top answer is really quite useful. Apparently it's not even a good thing to close all your apps at once. Someone else is also posting a screenshot with the icon you're mentioning by the way and says it closes all the apps for him. Quite strange that it doesn't do the same for me. Guess I'm on different firmware.
EDIT
Made a quick screencap of it. Same icon, different action.
While Googling I stumbled upon this though: http://android.stackexchange.com/qu...ckground-apps-at-once-in-android-5-0-lollipop
The top answer is really quite useful. Apparently it's not even a good thing to close all your apps at once. Someone else is also posting a screenshot with the icon you're mentioning by the way and says it closes all the apps for him. Quite strange that it doesn't do the same for me. Guess I'm on different firmware.
EDIT
Made a quick screencap of it. Same icon, different action.