/lib/udev/rules.d/60-tbtxdomain.rules is in thunderbolt-tools 0.9.3-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | # Thunderbolt udev rules for XDomain connections
SUBSYSTEM=="thunderbolt" ENV{DEVTYPE}=="thunderbolt_xdomain" ACTION=="add" RUN+="/lib/udev/tbtxdomain add $devpath"
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