  Attosecond charge migration is a periodic evolution of the charge density of
a molecule on a time scale defined by the energy intervals between the
electronic states involved. Here, we report the observation of charge migration
in neutral silane (SiH$_4$) in 690~as, its decoherence within 15~fs, and its
revival after 40-50~fs using X-ray attosecond transient absorption
spectroscopy. The migration of charge is observed as pairs of quantum beats
with a characteristic spectral phase in the transient spectrum. The decay and
revival of the degree of electronic coherence is found to be a result of both
adiabatic and non-adiabatic dynamics in the populated Rydberg and valence
states. The experimental results are supported by fully quantum-mechanical {\it
ab-initio} calculations that include both electronic and nuclear dynamics. We
find that conical intersections can mediate the transfer of electronic
coherence from an initial superposition state to another one involving a
different lower-lying state. Operating on neutral molecules, our methods define
a general approach to the key phenomena underlying attochemistry.
