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To flush blob cache on SharePoint servers you should execute a PowerShell script on each front end server. Blob cache is set on each front-end server in a farm, that is why you have to do this way.

Of course, you can use 'Invoke-Command' to execute script on other servers. The script to flush blob cache is here:

$webApp = Get-SPWebApplication "<WebApplicationURL>"
Write-Host "Flushed the BLOB cache for:" $webApp