Depending on temp and snow moisture content it's really easy for clingy snow to clump onto boot soles. Often this will happen after coming out of a warm lodge and getting back on skis, but it can happen anytime.
I've done the pole whack method, the binding scrape method - neither are reliable and are definitely not good for the equipment. What I do now is grab a pole down by the basket with the tip sticking out, use the other pole to help balance as I stand on one foot, then bend the boot out and up, (over the knee of the other leg, like the way a guy sits cross-legged), and thoroughly scrape the heel and toe clean with the pole tip. Click in after that without touching snow again, then repeat for the other boot.
I also have gotten into the habit of doing this.
Works for me.