Using C# (VS2010) with XNA 4.0, I have a terrain layer (RenderTarget2D) in a 2D side-scroller. My visual system tracks updates to redraw individual tiles, but I am having trouble finding a way to clear out the rectangle where the tile will be drawn, which I must do because A) there may no longer be a tile or B) the tile may itself contain transparency. How can I draw a rectangle of transparency onto an existing RenderTarget2D? I essentially want to clear just that rectangular portion of it. My Google searches have not yielded anything relevant.