  We present a mechanism for producing a cosmologically-significant relic
density of one or more sterile neutrinos. This scheme invokes two steps: First,
a population of "heavy" sterile neutrinos is created by scattering-induced
decoherence of active neutrinos; Second, this population is transferred, via
sterile neutrino self-interaction-mediated scatterings and decays, to one or
more lighter mass ($\sim 10\,{\rm keV}$ to $\sim 1\,{\rm GeV}$) sterile
neutrinos that are far more weakly (or not at all) mixed with active species
and could constitute dark matter. Dark matter produced this way can evade
current electromagnetic and structure-based bounds, but may nevertheless be
probed by future observations.
