Every now and then the icons in my Dock disappear completely after waking from sleep, except some of them go funny or fuzzy. See screenshot.
MacBook Pro Retina, 15", Mid 2014, i7, 16GB memory, often plugged into a Dell P2715Q 4K Display. El Capitan.
killall Dock in terminal to no avail, and rebooting doesn't do anything much.
Any thoughts on what's causing this, or how to force OS X to clear its cache of the icons or similar?