The recommended best practice for designing a domain hierarchy is to create a structure that is logical but not overly complex, typically 3-5 layers deep. This depth provides sufficient granularity for customer and data separation without creating excessive administrative overhead. The design must leverage the 'contains' relationship, which allows parent domains visibility into child domain data—a core function for Managed Service Providers (MSPs). Furthermore, the structure must include the system-provided 'default' domain, which is essential for housing global records and processes that are not assigned to a specific domain.

B. Using Service Offerings in the domain hierarchy

Service Offerings are data records (Configuration Items) that are domain-separated; they do not form the structural hierarchy of the domains themselves.

C. A domain heirarchy 3-5 layers deep that allows for use of contains if needed and does not contain a defualt domain

The 'default' domain is a mandatory, out-of-the-box component of the domain separation architecture and cannot be excluded from the hierarchy.

D. Having a totally flat domain heirarchy with no TOP domain

The 'TOP' domain is the mandatory root of any domain hierarchy; all other domains are its children. A hierarchy cannot exist without it.

E. Adding several domain layers below TOP before getting to the customer domain

While structuring layers between TOP and customer domains is common (e.g., for the MSP), this statement is less comprehensive than option A, which includes depth, 'contains' relationships, and the 'default' domain.

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1. ServiceNow Product Documentation - Domain Separation: The documentation states, "The domain hierarchy is the structure of all domains in an instance... The TOP domain is the parent of all other domains." It also explains, "The instance includes a default domain for records that are not assigned to a specific domain." This confirms the mandatory nature of TOP and default domains. (Refer to the "Domain hierarchy" and "Base system domains" sections in the Domain Separation documentation for the relevant ServiceNow release).

2. ServiceNow White Paper - Domain Separation Technical Best Practices: This guide often advises on hierarchy design, stating, "Keep the domain hierarchy as flat as possible to meet business needs... A deep hierarchy can be difficult to troubleshoot and maintain." A 3-5 layer depth is a common interpretation of this principle, balancing separation with manageability. (Refer to the section on "Domain Hierarchy Design").

3. ServiceNow Product Documentation - Domain separation options: The documentation details how data visibility works, which is directly tied to the 'contains' relationship inherent in the parent-child hierarchy. (Refer to the section "How domain separation works").