$item = Get-Item .
$options = @{}
[Sitecore.ContentSearch.ContentSearchManager]::Indexes | Foreach-Object { $options.Add($_.Name, $_.Name) }
$props = @{
    Parameters = @(
        @{Name="indexName"; Title="Choose an index"; Options=$options; Tooltip="Choose one."}
    )
    Title = "Index selector"
    Description = "Choose an index."
    Width = 300
    Height = 300
    ShowHints = $true
}
$result = Read-Variable @props
if ($result -eq "ok") {
    $indexName
    $index = [Sitecore.ContentSearch.ContentSearchManager]::GetIndex($indexName)
    [Sitecore.ContentSearch.Maintenance.IndexCustodian]::Refresh($index, [Sitecore.ContentSearch.SitecoreIndexableItem]$item)
}
Close-Window