Kinetics of three-dimensional normal grain growth and related processes (e.g., soap froth evolutions) described by the Mulheran--Harding model is studied. The model is represented by a diffusion equation with the grain--size--dependent diffusion coefficient. The equation is solved for an arbitrary initial distribution of grain sizes. It is proved that asymptotic kinetics do not depend on the initial state.

PACS numbers: 05.40.--a, 64.60.--i, 81.10.Jt