Assuming you mean clear the apps out of the multitasking screen, no, there is no way to do that on stock Android. Possibly if you were to root your phone, but not out of the box.
CF put out an app called Recents that will add a clear all as well as adjusting the number of apps allowed and time they can remainin in multitasking, requires root.
It seems like the N6P is handling memory pretty well so I am trying to wean myself off closing all the apps out. Not sure if its thanks to the 3GB of ram or what but I do not see any lag even with 10-20 apps open.