How to copy an action strip from one object to another? I have those two identical armatures. I would like to copy a part of one's animation to the other. I came up with the idea of making an action strip and then I'll copy it. As shown in the pic, I need to copy a3 to the second object.

I used the method of CTRL+L > Animation Data. But copies everything and it affects a2.  Affecting a2 means that in larger projects it'll affect all the strips which isn't a good idea.

I appreciate your ideas :)
Assuming, both armatures have same bone names (etc) 
just did a quick test, NLA editor won't let you copy action strips from one object to another via dragging / moving (G key) .

Option 1 (shift + A) in NLA editor will let you pick action as well


Option 2 (as shown in image)
Right now, best way to do is to use 'Action Editor' in Dope Sheet Area. Just use the action there on armature and then use it in NLA