Asbestos cement shingles contain about 1% asbestos. The reason they were made was because of their resistance to fire. Hence, the asbestos in it.
Certainly, the asbestos shingles are classified as 'non-friable'. This means that the danger becomes 'apparent' when the shingles become frieable. IE., they're a 'solid' material and is only hazardous when they're broken up. So, if you ever go removing them to install, say, vinyl siding, don't go smashing them up! It will generate a lot of dust that can cause more problems then you bargained for.
In this particular case, you do want to clean the shingles. Power-wash them from 'above'; NOT from below. If you do it from above, you may get water UNDER the shingles (which will do its own damage), or you may blow them off the wall. Of course, use low pressure. You may get away with using a garden hose but if you have a well, I guarantee you'll want more pressure. If your shingles were never painted by you before, you do want a primer (as with painting any other 'previously unpainted surface'.) Stop by your local PAINT RETAILER for information on Priming and Painting. Ask them for a recommendation. There are paints especially made for this type of surface. My entire development (27 years old), was originally built with these shingles. Slowly, the neighbors are replacing them with vinyl. (It helps with value.) If you are ever considering the same, post up and we can 'guide' you.
Remember, the most important part of this job is PREPARATION! (Painting is the EASY part.) My best to ya and hope this helps.
PS: Wire brushing the shingles WILL cause the shingles to 'release' some asbestos. Brush sparingly. And if necessary, wear a mask.