And today I cleaned 2 rugs and tomorrow I'm doing 3 more. It was very easy and satisfying, although I needed help with the rugs because they are heavy.
Here are the steps:
1) put your rug outside for 1/2 hour or so to make it cold (you don't want it to melt the snow).
2) spread it face down in snow and beat on the back until you're really tired. Sprinkle some snow on the back and sweep it off. Then, turn it over into a different patch of snow. If it leaves a lot of dirt behind, you can turn it facedown and beat it some more, and then sweep it with snow some more. But once might be enough.
Below is a picture of the filthy snow, after beating the rug upside down.
3) With the rug face up sweep all the snow off. Then put more snow on it and sweep that snow off.
4) Shake it, if it's small enough, or do some fancy sweeping to get most of the snow off and leave it in the garage or the porch so the remaining snow can magically disappear in a process called sublimation. (At least that's what it says on the internet.)
This process is supposed to produce leave the colors in your wool rugs looking brighter. I've done 2 now (3 to go, tomorrow) and I think it's true. They look clean and they smell nice - not that dusty smell rugs often have. It's a little hard to capture the color in a photo. But it's nice.
Here is a picture from flicker of some women in the Ukraine doing this - Click here to see the picture, entitled Women Beating Rugs in the Snow - Lutsk, Ukraine, 1998 by Robert Nagle.