This command permanently destroys (purges) previously deleted builds. No build artifacts will be deleted. Syntax - TfsBuild ...

This command permanently destroys (purges) previously deleted builds. No build
artifacts will be deleted.

Syntax -
TfsBuild destroy /collection:teamProjectCollectionUrl
                 /buildDefinition:definitionSpec buildNumber [buildNumber ...]
                 [/noPrompt] [/silent] [/preview]
   or
TfsBuild destroy /collection:teamProjectCollectionUrl buildUri [buildUri ...]
   or 
TfsBuild destroy teamProjectCollectionUrl teamProject buildNumber
                 [buildNumber ...]
   or
TfsBuild destroy /collection:teamProjectCollectionUrl /dateRange:[date]~[date]
                 /buildDefinition:definitionSpec
   or
TfsBuild destroy /collection:teamProjectCollectionUrl /dateRange:[date]~[date]
                 teamProject

teamProjectCollectionUrl    The url to the Team Project Collection used for build(s).
definitionSpec              The specification of the build definition(s) containing
                            the build(s) to be destroyed. Wildcards are supported.
buildNumber                 The build number in the Team Project to be destroyed.
                            Wildcards are supported.
buildUri                    The Uri of the build to be destroyed.
teamProject                 The team project used for build(s).
date                        A date, formatted in any .NET parsable format.
[/noPrompt]                 Do not prompt while deleting the build(s).
[/silent]                   Do not write output to the console while destroying. 
                            Implies /noPrompt.
[/preview]                  Preview the builds selected for destroying. Does not
                            destroy any builds.