We study the vibrational decoherence dynamics of an iodine molecule in a finite krypton cluster comprising the first solvation shell. A normal mode analysis allows us to successively increase the complexity of the description. For the ground state dynamics, comparison with experimental matrix results shows that already four degrees of freedom are sufficient to capture the main decoherence mechanism. For electronically excited iodine, we model the vibrational dynamics of initial Schrödinger cat-like states by the semiclassical hybrid dynamics [F. Grossmann, J. Chem. Phys. 125, 014111 (2006)] and full quantum calculations, where available. Good agreement of the results is found for a reduced model with three degrees of freedom. We find non-Gaussian distortions of the bath density matrix, which is a necessary condition, if Schrödinger cat-like states in the bath are to be identified. However, in contrast to the experiment [D. Segale et al., J. Chem. Phys. 122, 111104 (2005)], we observe only incoherent superpositions of bath vibrational states.