You can use the DomainDeny property of the IIsIPSecurity object to edit lists of domains that are not allowed access to the server.
SecObj.DomainDeny Domain
<%
Dim SecObj
Dim MyIPSec
Dim IPList, DomainList
Set SecObj = GetObject("IIS://LocalHost/W3SVC/1")
Set MyIPSec = SecObj.IPSecurity
'Test value of MyIPSec.GrantByDefault here.
DomainList = MyIPSec.DomainDeny
IPList = MyIPSec.IPDeny
Redim IPList (Ubound(IPList)+1)
IPList (Ubound(IPList)) = "123.0.0.1,255.255.255.0"
Redim DomainList (Ubound(DomainList)+1)
DomainList (Ubound(DomainList)) = "somedomain.com"
IPSec.DomainDeny = DomainList
IPSec.IPDeny = IPList
Set SecObj.IPSecurity = MyIPSec
Ojb.Setinfo
%>
IPDeny, IPGrant, DomainGrant, GrantByDefault, IIsIPSecurity