  The Breakthrough Listen search for intelligent life is, to date, the most
extensive technosignature search of nearby celestial objects. We present a
radio technosignature search of the centers of 97 nearby galaxies, observed by
Breakthrough Listen at the Robert C. Byrd Green Bank Telescope. We performed a
narrowband Doppler drift search using the turboSETI pipeline with a minimum
signal-to-noise parameter threshold of 10, across a drift rate range of $\pm$ 4
Hz\ $s^{-1}$, with a spectral resolution of 3 Hz and a time resolution of
$\sim$ 18.25 s. We removed radio frequency interference by using an
on-source/off-source cadence pattern of six observations and discarding signals
with Doppler drift rates of 0. We assess factors affecting the sensitivity of
the Breakthrough Listen data reduction and search pipeline using signal
injection and recovery techniques and apply new methods for the investigation
of the RFI environment. We present results in four frequency bands covering 1
-- 11 GHz, and place constraints on the presence of transmitters with
equivalent isotropic radiated power on the order of $10^{26}$ W, corresponding
to the theoretical power consumption of Kardashev Type II civilizations.
