Update how-to-cache-purge-powershell.md

[BrandynR-MSFT]

Add clarification to Azure PowerShell usage for Azure Front Door purging

https://learn.microsoft.com/en-us/powershell/module/az.cdn/clear-azfrontdoorcdnendpointcontent?view=azps-12.4.0 The -Domain is an optional parameter, however since Azure Front Door using wildcard domains doesn't support purging similar to '*.contoso.com', you must specify a subdomain. Current wording with an 'Optional Parameter' makes it seem as not specifying a -Domain would purge the wildcard domain (which isn't supported). Omitting the subdomain would only clear the Endpoint cache of example.azurefd.net as its not clarifying when the operation occurs.

[prmerger-automator[bot]]

@BrandynR-MSFT : Thanks for your contribution! The author(s) have been notified to review your proposed change.

[learn-build-service-prod[bot]]

Learn Build status updates of commit aef5c5f:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
articles/frontdoor/standard-premium/how-to-cache-purge-powershell.md	:white_check_mark:Succeeded

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel

[Jak-MS]

@duongau Can you review the proposed changes?

Important: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

label:"aq-pr-triaged"

@MicrosoftDocs/public-repo-pr-review-team