Wool is such cool stuff--It has sort of scales on the outside of each fiber. Warm water opens them up and if they are agitated while the scales are open then the fibers will enmesh with each other. From our perspective this is felting.

If you get the wool hot but don't slosh it around then the scales just go back where they were without hooking up with their neighbors.

To sum up: Higher temps are ok. Higher temps + agitation may cause felting.

Some wool is treated chemically to change the structure, but with such a pretty jersey, why risk it?