It’s possible to write directly to the rendered image data using putImageData. By creating new image data then assigning it to the canvas, you will clear the entire screen.

var imageData = ctx.createImageData(canvas.width, canvas.height);
ctx.putImageData(imageData, 0, 0);

Note: putImageData is not affected by any transformations applied to the context. It will write data directly to the rendered pixel region.