Cleaning a WebGLRenderTarget

Hello, I’m making an application that implement a ping pong buffer technique.

I want that a certain moment, for example when I press a certain key, the first buffer (in the sketch, the textureA) is cleaned, and for cleaned I mean it becomes black, and it does not contain the image of the feather anymore. At this point the content of the buffer A should be copied in buffer B, and there should be only the feather visible, without the trails

What I’ve tried was to use textureA.dispose(), as explained in the doc, but this did not clear the texture, it simply dispatched a dispose event.
What is the simplest way to clear it? should I draw a black square in the textureA WebGLRenderTarget?

Would make sense, to pass a black texture to the webGLRenderTarget?