  Extragalactic and galactic cosmic rays scatter with the cosmic neutrino
background during propagation to Earth, yielding a flux of relic neutrinos
boosted to larger energies. If an overdensity of relic neutrinos is present in
galaxies, and neutrinos are massive enough, this flux might be detectable by
high-energy neutrino experiments. For a lightest neutrino of mass $m_{\nu} \sim
0.1$ eV, we find an upper limit on the local relic neutrino overdensity of
$\sim 10^{13}$ and an upper limit on the relic neutrino overdensity at TXS
0506+056 of $\sim 10^{10}$. Future experiments like GRAND or IceCube-Gen2 could
improve these bounds by orders of magnitude.
