Whenever possible use both label and icon
Why ? There are plenty of naive users out there. For them an icon can mean anything. For someone used to application he/she may understand that it is a reset button.
But there is always chance of confusion with naive users. It can be refresh or something else too.
Usually applications should use icon alone when they have a real estate problem. From your layout i assume that you have enough real estate to add a button that says rest. You can also add an icon to the right of the button.
Icons are helpful in case where people of different language are using your application. So whenever possible icons should be an addition or fallback option. Not the primary way of identification.