A function to force a reset of the health state for an agent in Operations Manager 2012 SP1 and a function to remove a management gorup

Reset-HealthState.ps1

Function Reset-HealthState
{
  param
  (
    $AlertName,
    $ResolutionState
  )
  $Criteria = "Name like '$($AlertName)' and ResolutionState != $($ResolutionState)"
  $Alerts = Get-SCOMAlert -Criteria $Criteria

  ForEach($Alert in $Alerts)
  {
    $Monitor = Get-SCOMMonitor -Id $Alert.MonitoringRuleId
    Get-SCOMClassInstance -id $Alert.MonitoringObjectId | foreach {$_.ResetMonitoringState($Monitor)}
    }
}

Function Remove-ManagementGroup
{
#
# http://msdn.microsoft.com/en-us/library/hh329017.aspx
#
param ([string]$ManagementGroup)
$opsConfig = New-Object -ComObject AgentConfigManager.MgmtSvcCfg
$opsConfig.RemoveManagementGroup($ManagementGroup)
Restart-Service healthservice
}

See http://www.system-center.me/opsmgr/reset-monitor-state-with-powershell for more details

Just updated this to change the param MonitorName to AlertName since that's what we're really after here. Once we have the alerts then we pull the monitor Id from there.