These Cobblestones can be sealed with an invisible penetrating sealer to assist in the ongoing clean up of the stone. An invisible penetrating sealer can be applied prior to grouting which will facilitate easy clean up after application of the grout.
Do not use Hydrochloric acid for clean up as this can cause minerals present in the stone to react.
Just sweep when needed. These Cobblestones respond well to high pressure cleaning. A solution of mild detergent and water, can be applied prior to pressure cleaning.