Reset expression

I'm reasonably certain there are scripts on AEScripts.com that can do that for some common properties, but I doubt you'll find something that covers everything, since those values also would have to be hard-coded in the script for some properties.

Mylenium 

Expressions cannot do that. The evaluation order is still Property Value --> Keyframes --> Expression, so an expression will always use what the previous value is or what it has in it's code. Of course you could encode the values in the expression itself, but that would have to be done for each property type individually and even then it wouldn't actually reset the values. All that being the case, you still have to go through all your layers and use the reset options on transform properties, effects and so on.

Mylenium