  We explore the validity of the generalized second law (GSL) of thermodynamics
in flat FRW universe with apparent horizon and event horizon as the boundary.
We found that in a universe with holographic Ricci dark energy and dark matter,
interacting with each other, the GSL is satisfied at the apparent horizon and
partially satisfied at the event horizon under thermal equilibrium conditions.
We also analyses the GSL under non-equilibrium conditions and shows that the
fulfillment of GSL at the apparent horizon implies that the temperature of the
dark energy is greater than that of the horizon. Thus there occurs a flow of
dark energy towards the apparent horizon. As a result the entropy of the dark
energy decreases and that of horizon increases. This is verified by finding the
evolution of the dark energy entropy and horizon entropy in a dark energy
dominated universe under non-equilibrium conditions.
