sudo rm -rf /Library/Caches/com.apple.iconservices.store
sudo find /private/var/folders/ -name com.apple.dock.iconcache|xargs rm -rf
sudo find /private/var/folders/ -name com.apple.iconservices|xargs rm -rf
then run command [sync] and [reboot] to reboot system, after all, the icon caches will be refreshed.