These answers are all useful, but sometimes I think people overthink the Dramatica terminology to a point where it causes confusion.
Lately for me I've been trying to focus more on the feel or "personality" of the story to identify/understand the throughlines. In Dramatica, Domain is the thing that most associated with genre, which is a little different from "genre" as conventionally understood, but still useful. If you watch a bunch of movies that have the same OS Domain, you'll start to get a feel for why they're similar, especially if you read the analyses.
So usually, the OS of an action-adventure or superhero movie will be in Physics, because at some level this is just what the movie is about -- external actions and the conflict that comes about from them. Psychological thrillers are most often in Psychology, for obvious reasons, as are romantic coming of age stories because they're both usually "about" people manipulating and/or trying to convince each other and themselves of things (rather than trying to kill each other).
OS Mind stories are often about prejudice, but also just being stuck in a certain mindset. Once you start comparing movies and books from that perspective, the Domains are often obvious just based on the feel of the movie.
There are apparent exceptions, but even these have a reason. Is The Incredibles really a superhero story? Or is it really a family drama (Psychology) told in the form of a superhero story? It The Fugitive really an action-adventure story, or is it more about the imbalance in the Universe caused when someone is wrongly accused?
On another thread recently someone mentioned that The Wizard of Oz is a Mind story. I hadn't thought about that before, but it totally makes sense, doesn't it? All of the characters are completely stuck in mindsets and prejudices -- about themselves and others (and about places -- who wants to live in Kansas, ugh.)
12 Angry Men is a courtroom drama. I guess you could write a courtroom Drama as a Physics story (will the jury be able to Learn and Understand what actually happened?) or a Psychology story (will the prosecutor succeed in manipulating the jury to convict an innocent man?) But when you really think about it, 12 Angry Men is obviously a Mind story--everyone is totally stuck in preconceived notions and prejudices that if not corrected will have disastrous consequences for the accused.
Of course I still doubt myself. I just read Fahrenheit 451 and came away with the strong sense that it's an OS Mind story, but I won't trust myself until someone agrees to work though it with me on a thread.