Do you mean a CBN wheel, typically a reddy brown colour? If so just use it to grind a sharpening stone like an oil stone. If you mean the type that fits an angle grinder just use it to grind a soft brick or soft concrete block.
There seems to be a few ways to clean both diamond impregnated wheels and CBN, washing, using a cleaning block. Cleaning block seems to be aluminium oxide. Have both types of wheel but not cleaned either yet!!