Background:

I have an environment with two different AD domains, each in its own forest, each with two Windows Server 2008 R2 domain controllers acting as DNS servers. There is no trust between the domains.

Each DNS server manages the main DNS zone for its AD domain, and then some other zones, including the reverse lookup zone for its IP subnets; all zones are AD-integrated; all DNS servers which manages a zone are correctly listed as authoritative name servers for that zone.

So, the situation is like this (using fake names and IP addresses):

Domain A:
DNS domain: a.dom
IP subnet: 192.168.1.X
DC/DNS Servers: serverA1.a.dom (192.168.1.1) and serverA2.a.dom (192.168.1.2)
Authoritative zones: a.dom, 1.168.192.in-addr.arpa, somezone.local

Domain B:
DNS domain: b.dom
IP subnet: 10.0.0.X
DC/DNS Servers: serverB1.b.dom (10.0.0.1) and serverB2.b.dom (10.0.0.2)
Authoritative zones: b.dom, 0.0.10.in-addr.arpa, someotherzone.local

DNS servers in domain A have conditional forwarders defined for each zone managed by DNS servers in domain B, forwarding to both domain B's DNS servers; DNS servers in domain B have the opposite configuration. All forwarders are stored in Active Directory.

All is working perfectly, and computers in each domain can resolve forward and reverse DNS queries for both domains, using their domain's DNS servers.

The problem:

I have SCOM 2012 deployed in domain A, with the SCOM agent installed on both DCs; the management packs for Active Directory and DNS Server are installed and up-to-date.

I have a series of alerts like the following ones on both domain controllers; each alert is generated for each forwarded zone and for each forwarded server:

Forwarder someotherzone.local (10.0.0.1) cannot resolve the host name 192.168.1.1,someotherzone.local for serverA1.a.dom
Forwarder someotherzone.local (10.0.0.2) cannot resolve the host name 192.168.1.1,someotherzone.local for serverA1.a.dom
Forwarder someotherzone.local (10.0.0.1) cannot resolve the host name 192.168.1.2,someotherzone.local for serverA2.a.dom
Forwarder someotherzone.local (10.0.0.2) cannot resolve the host name 192.168.1.2,someotherzone.local for serverA2.a.dom
Forwarder 0.0.10.in-addr.arpa (10.0.0.1) cannot resolve the host name 192.168.1.1,0.0.10.in-addr.arpa for serverA1.a.dom
Forwarder 0.0.10.in-addr.arpa (10.0.0.2) cannot resolve the host name 192.168.1.1,0.0.10.in-addr.arpa for serverA1.a.dom
Forwarder 0.0.10.in-addr.arpa (10.0.0.1) cannot resolve the host name 192.168.1.2,0.0.10.in-addr.arpa for serverA2.a.dom
Forwarder 0.0.10.in-addr.arpa (10.0.0.2) cannot resolve the host name 192.168.1.2,0.0.10.in-addr.arpa for serverA2.a.dom

The only exception is the main AD DNS zone managed by domain B's DNS servers (b.dom): for that conditional forwarder, no alert is generated and the forwarder availability monitor is green.

Ok, what does this mean?
What are those monitors trying to tell me?
What are they checking?
What's actually wrong?

And why there is no error for the "b.dom" zone, which is configured in the exact same way as the other ones, both as a zone in domain B's DNS servers and as a forwarder in domain A's DNS servers?