[Xmonad] How do I know if Xinerama's working?

I've just built X11-extras and xmonad, largely without incident, and Xinerama seems not to be working: when I create an xterm, it spans both screens. Is that to be expected? I was expecting each screen to contain its own workspace. There's no problem with my X.org setup in general: I have a libXinerama.so.1, and (for example) ion3 links against it and seems to use it. (xmonad doesn't link against it, according to ldd, but I'm not sure whether I should expect it to or not.)