Syncing Password of selected OU/subdomain

Hi,

We are migrating one of our child domains to Office365. We want to use Azure AD Sync tool to sync password of our child domain users to Azure AD. I understand we have to sync all accounts to make GAL on Office365 identical to On-premises GAL but is it possible to sync password of only a sub-domain or OU specific users and not of entire forest?

Thanks

Rafay