Jenkins Pull Request Builder issue when serving two github enterprise instances?

Multi tool use
Jenkins Pull Request Builder issue when serving two github enterprise instances?
We hosted 2 different github instances, say, one is configured as http://git.domain1.com/ while the other http://git.domain2.com/.
Then on a same Jenkins server, I set up 2 jobs for 2 different repos, respectively. One repo is from domain1 and the other from domain2.
Both jobs are configured to Use github hooks for build triggering.
Now the problem is, pull request from either repo will simply trigger both Jenkins jobs to run. So there is always one build making no sense at all and is doomed to fail.
I guess it was partly because both repoes are configured with exactly the same hook url: http://our-jenkins.com:8080/ghprbhook/ (but we do have only one Jenkins server).
Another part of the reason may be "Use github hooks for build triggering", which makes the jobs simply wait for hook request passively, without honoring what I configured in "Project URL" and "Repository URL".
But how can I get out of this situation?
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