Sometimes there is need to perform “deep” reset of entire IIS envirionment. To do so You can use powershell script:

$CRMSnapin = 'Microsoft.CRM.PowerShell';

if ( (Get-PSSnapin -Name $CRMSnapin -ErrorAction SilentlyContinue) -eq $null )
{
    Add-PSSnapin $CRMSnapin
}

#iisreset

# Recycle only CRM Application Pool to free dlls.
C:\Windows\System32\inetsrv\appcmd recycle apppool /apppool.name:CRMAppPool
C:\Windows\System32\inetsrv\appcmd recycle apppool /apppool.name:CrmDeploymentServiceAppPool

# Reset service responsible for invoking asynchronous plugins and workflows
net stop MSCRMAsyncService
net stop MSCRMSandboxService
net stop MSCRMUnzipService

net start MSCRMAsyncService
net start MSCRMSandboxService
net start MSCRMUnzipService