Another good litmus test is to just take the scene out and see what that does. Sometimes adding a single line of dialogue somewhere else can serve the purpose of a few unnecessary scenes.

My first line of attack--if I have any doubt I take it out. There's always those scenes where you know, but don't want to admit, are useless. I just drop them.

Later when I'm wrestling with it again and again I ask myself questions like you suggested.

Patrick's suggestion is one I've found useful too.

Someone needs to forward this article to Christopher Nolan immediately.

Agree with Patrick's approach. Probably, if I've gone to this length, the scene is unnecessary. And, sure enough, there's a tighter sequence in front of me.

Author Lawrence Block's 'Telling Lies for Fun and Profit' is a treasure chest of good advice on writing. He tells of someone who was visiting a company that traded in flour. A sign on the wall said, "Does it sell flour?" Implying that if it didn't, "to hell with it." Block adapated it to "Where's the story?" If what he's typing isn't advancing the story, it should be cut. That's an apt approach for scenes. If the scene isn't moving the story forward in some identifiable way, get rid of it. Even if it's a really good, well written scene, you must "kill your darlings." Does the scene sell flour?