We report an extensive computational investigation on the dynamics of a simple bead−spring model for melts of diblock (AB) copolymers. Monomer displacements, end-to-end and bond reorientations, as well as relaxation of chain normal modes, are characterized both in the homogeneous phase and in the limit of strong segregation. In the latter case, the B-blocks are aggregated into “micellar-like” spherical domains. We investigate the case in which the B-homopolymer exhibits a much higher glass transition temperature than the A-homopolymer, and thus an intrinsically much slower mobility. In such conditions, the interplay between a strong interfacial barrier suppressing diffusion and a highly mobile surrounding corona induces a soft confinement effect on the B-blocks forming the spherical cores. The spontaneously formed spherical phase is highly polydisperse in the micellar aggregation number. However, this is a minor source of dynamic heterogeneity in comparison to the specific location of the monomer along the chain. The time scales for bond reorientation exhibit extreme differences between bonds close to the micellar interface and those close to the chain ends. The comparison of orientational correlators and normal modes for the B-component in the diblock system and in the homopolymer state reveals scaling behavior. Results are rationalized within the Rouse model, for intermediate time scales not probing the interface, through a change in the effective friction with the temperature and the energy scale of the A−B interaction. We acknowledge financial support from the projects NMP3-CT-2004-502235 (SoftComp, EU), MAT2007-63681 (Spain), 2007-60I021 (Spain), and IT-436-07 (GV, Spain). Peer reviewed