Houdini Octane

Shadow catcher with diffuse bounce

I think default shadow catching doesn't get the bounce so you can whip it up with a rayswitch. I sort of plugged stuff into stuff for it to work (topright pigheads -- bottom left is normal shadowcatcher,plane grid is a green material):

(also i cropped the rayswitch like an idiot but camera ray is at 0 the rest at 1

Double sided material in Octane

You can use tool_polygon_side to drive a material mixer: