Jenkins - poll multiple GIT repos at a time and perform all steps in parallel

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Groovy

Jenkins

Consider I have 3 Repos, RepoA, RepoB and RepoC.

In Jenkins Pipeline I want to perform individual builds for all the 3 Repos only if there is a recent check-in. (These are 3 repos but the solution is inter dependent).

Stages are like below

stages {
        stage ('Build') {
            ....
        }
        stage ('UnitTest') {
            ....
        }
        stage ('Deploy') {
            ....
        }
    }

All I want is to run 3 stages at once or in parallel if multiple Repo detects changes (Check-in done in RepoA and RepoB only (Consider)). How can this be achieved in Jenkins pipeline?

What I have tried:

clueless to find a solution for this.