  We consider the reduced density matrix (RDM) \rho_A(t) for a finite subsystem
A after a global quantum quench in the infinite transverse-field Ising chain.
It has been recently shown that the infinite time limit of \rho_A(t) is
described by the RDM \rho_{GGE,A} of a generalized Gibbs ensemble. Here we
present some details on how to construct this ensemble in terms of local
integrals of motion, and show its equivalence to the expression in terms of
mode occupation numbers widely used in the literature. We then address the
question, how \rho_A(t) approaches \rho_{GGE,A} as a function of time. To that
end we introduce a distance on the space of density matrices and show that it
approaches zero as a universal power-law t^{-3/2} in time. As the RDM
completely determines all local observables within A, this provides information
on the relaxation of correlation functions of local operators. We then address
the issue, of how well a truncated generalized Gibbs ensemble with a finite
number of local higher conservation laws describes a given subsystem at late
times. We find that taking into account only local conservation laws with a
range at most comparable to the subsystem size provides a good description.
However, excluding even a single one of the most local conservation laws in
general completely spoils this agreement.
