Cannot remove network devices

Hello

I have SCOM 2012 R2.

I'm trying to remove discovered network devices, but I'm not getting.

I already tried to:

• Delete Discovery Rule
• Delete Network Devices in Administration\Network Management\Network Devices
• Export, delete and import Microsoft.SystemCenter.NetworkDiscovery.Internal MP

But the my network devices continue to be displayed grayed in Monitoring\Networ Monitoring\Network Devices.

If I create a discovery rule and try rediscover, network devices are duplicated.

Can someone help me?

Thanks,

Marcos