emacs scroll other window up

You can alternatively give a negative argument to C-M-v. Negative arguments can be given with almost any modifier combination. In that case you can type C-M-- C-M-v.

On many terminals you can do M-PageUp and M-PageDn to scroll the other window. It's nice if you're already used to using PageUp/PageDn for scrolling.

Try C-M-S-v, which is scroll-other-window-down.

You can find such key bindings by doing C-h b (describe-bindings) which populates the *Help* buffer with a list of all the key bindings and associated commands for the current buffer. A quick search through that for scroll-other showed the binding you mentioned, as well as the one I listed.